THE COURSE OF INFECTION 137 



(6) Upon the site of infection. Thus the introduction of rabies 

 virus or of tetanus bacilli into the tissues of the face or into a deep wound 

 is likely to be followed by a shorter period of incubation than when 

 these are introduced into the foot or in superficial wounds. 



(c) Upon the degree of resistance offered by the host. For instance, 

 one individual may contain more antitoxin or bacteriolysin for a certain 

 bacterium than another, and consequently a longer period of incubation 

 is required, during which these substances are neutralized and an excess 

 of toxic bacterial substance is produced. In fact, these may offer such 

 resistance to the bacterium that the process of infection is inhibited, or 

 but slight and evanescent disturbances appear. 



(d) Upon the general susceptibility of the host and the route of in- 

 vasion. 



2. The period of prodromal symptoms, characterized by systemic 

 disturbances of a relatively mild type, due to diffusion of the bacteria 

 and their products into the general circulation and their wide-spread 

 effect upon the body-cells in general. If the bacteria select a special 

 tissue or organ for attack, as the typhoid bacillus for lymphoid tissue, 

 and pneumococci .for the lungs, definite symptoms develop later, their 

 nature depending on the special tissue or organ involved. The pro- 

 dromata, however, are more marked, and indicate a wide-spread but 

 mild action upon the body-cells in general. Vaughan believes that these 

 symptoms mark the time when sufficient proteolytic ferments have been 

 generated by the body-cells against the new bacterial protein of the 

 invading bacteria to attack the latter, splitting the molecule and liberat- 

 ing a toxic moiety responsible for the general symptoms of intoxication. 



3. The period of fastigium, or of high fever, during which the disease 

 is at the height of its severity. Special and distinctive symptoms and 

 lesions, according to the organ or organs especially involved, are present; 

 the struggle between the offensive and defensive forces of parasite and 

 host is at its height, with remissions or exacerbations dependent upon 

 the supremacy of any one of these, and the general stability of the body- 

 cells in withstanding the wear and tear. During this time the protect- 

 ive proteolytic ferments of Vaughan are most active in disrupting the 

 newly formed bacterial protein, with the liberation of the toxic portion. 

 This process may be so active as to overwhelm the host with the toxic 

 split product, or lead to grave secondary lesions, such as extensive necro- 

 sis, perforation of a viscus, or hemorrhage. 



4. The period of decline, during which the patient is gradually over- 

 coming the infection, and amelioration of the symptoms takes place. 



